Epigenetic modifications, especially alterations in DNA methylation in promoter regions of genes, are increasingly being recognized as key factors in the pathogenesis of a wide variety of complex disorders. We propose to investigate the association of global DNA methylation patterns in circulating monocytes in relation to atherosclerosis and monocyte gene expression profiles in the Multi-Ethnic Study of Atherosclerosis (MESA). DNA and RNA will be purified from monocytes isolated from blood samples of a large sample (n=1600) of MESA subjects (44-85 year old, 40% Whites, 27% Blacks, and 21% Hispanics) who are free of clinical atherosclerotic cardiovascular disease (ASCVD) and scheduled to undergo quantitative ultrasound assessment of carotid artery intimal-medial thickness (IMT) and computed tomography-determined calcified coronary plaque at MESA exam 5 (in 2010-2011). The DNA samples will be used to determine genome-wide DNA methylation profiles in a random 1/2 (800) of the participants. Commercial platforms will be used to assay methylation of approximately 27,000 CpG sites covering more than 14,000 well-annotated genes and most CGIs in the genome. RNA from the same monocytes will be used to perform expression profiling of ~25,000 genes, of which more than 12,700 are also present on the methylation assay. Associations between DNA methylation patterns and the extent of atherosclerosis measured by carotid IMT will be determined. Integrative analyses will be performed to elucidate the connections between DNA methylation markers and cellular mRNA expression of cognate genes. Follow-up studies will be performed on subsets of these genes in the remaining cohort to verify DNA methylation/mRNA transcript relationships and their associations with subclinical atherosclerosis. Genomic regions representing confirmed associations will be subsequently investigated using 540 MESA subjects (selected from the 1600 MESA participants) with extremes of IMT phenotypes to reveal functional implications. The proposed studies utilizing this unique and well characterized population will transform the understanding of the role of epigenomics and DNA methylation in relation to atherosclerosis and ASCVD. The knowledge obtained should yield new biomarkers for ASCVD diagnosis and uncover unique therapeutic targets for future targeted interventions. Public Health Relevance: Atherosclerotic cardiovascular disease (ASCVD) remains one of the leading causes of morbidity and mortality world-wide. We propose to investigate the epigenomics of ASCVD through mapping of monocytic DNA methylation profiles. This interdisciplinary, cooperative work will transform our understanding of the etiology and severity of ASCVD.